[PATCH 4.16 086/161] loop: fix LOOP_GET_STATUS lock imbalance

From: Greg Kroah-Hartman
Date: Thu May 24 2018 - 05:10:02 EST


4.16-stable review patch. If anyone has any objections, please let me know.

------------------

From: Omar Sandoval <osandov@xxxxxx>

commit bdac616db9bbadb90b7d6a406144571015e138f7 upstream.

Commit 2d1d4c1e591f made loop_get_status() drop lo_ctx_mutex before
returning, but the loop_get_status_old(), loop_get_status64(), and
loop_get_status_compat() wrappers don't call loop_get_status() if the
passed argument is NULL. The callers expect that the lock is dropped, so
make sure we drop it in that case, too.

Reported-by: syzbot+31e8daa8b3fc129e75f2@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 2d1d4c1e591f ("loop: don't call into filesystem while holding lo_ctl_mutex")
Signed-off-by: Omar Sandoval <osandov@xxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
drivers/block/loop.c | 33 ++++++++++++++++++---------------
1 file changed, 18 insertions(+), 15 deletions(-)

--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1287,12 +1287,13 @@ static int
loop_get_status_old(struct loop_device *lo, struct loop_info __user *arg) {
struct loop_info info;
struct loop_info64 info64;
- int err = 0;
+ int err;

- if (!arg)
- err = -EINVAL;
- if (!err)
- err = loop_get_status(lo, &info64);
+ if (!arg) {
+ mutex_unlock(&lo->lo_ctl_mutex);
+ return -EINVAL;
+ }
+ err = loop_get_status(lo, &info64);
if (!err)
err = loop_info64_to_old(&info64, &info);
if (!err && copy_to_user(arg, &info, sizeof(info)))
@@ -1304,12 +1305,13 @@ loop_get_status_old(struct loop_device *
static int
loop_get_status64(struct loop_device *lo, struct loop_info64 __user *arg) {
struct loop_info64 info64;
- int err = 0;
+ int err;

- if (!arg)
- err = -EINVAL;
- if (!err)
- err = loop_get_status(lo, &info64);
+ if (!arg) {
+ mutex_unlock(&lo->lo_ctl_mutex);
+ return -EINVAL;
+ }
+ err = loop_get_status(lo, &info64);
if (!err && copy_to_user(arg, &info64, sizeof(info64)))
err = -EFAULT;

@@ -1530,12 +1532,13 @@ loop_get_status_compat(struct loop_devic
struct compat_loop_info __user *arg)
{
struct loop_info64 info64;
- int err = 0;
+ int err;

- if (!arg)
- err = -EINVAL;
- if (!err)
- err = loop_get_status(lo, &info64);
+ if (!arg) {
+ mutex_unlock(&lo->lo_ctl_mutex);
+ return -EINVAL;
+ }
+ err = loop_get_status(lo, &info64);
if (!err)
err = loop_info64_to_compat(&info64, arg);
return err;